ctDNA as surveillance monitoring in clinical progressors. The results of ctDNA detected in stored serum samples collected after therapy compared with conventional monitoring for clinical relapse with periodic clinic visits and regular CT scans. (A) Serum samples collected after therapy in 8 patients who achieved CR, underwent surveillance, and then clinically progressed. The assigned patient numbers are to the left. Histology: patient 9, PTCL-NOS; patients 180, 291, and 317, AITL; patients 190 and 200, ALK⁺ ALCL; and patients 198 and 274, PTCL-TFH. (B) The pattern of fluctuation of quantitative ctDNA levels of patients 9 and 198 with persistently detectable ctDNA before clinical relapse. The x-axis represents time since the on-study date in months and is different for each graph. The y-axis represents the log10 of the quantity of each dominant clonotype (in clonotypes per milliliter). Each colored line represents a different clonotype. The horizontal gray line represents the median level of baseline ctDNA. The dashed vertical line represents EoT, the red vertical line represents time of progression . The green horizontal bar represents time in clinical remission, and the red horizontal bar represents time after progression.